TOP特別プログラム
 
プレナリーレクチャー2
PL2
Co-operation of Distinct Cell Types in Network State-dependent Activity of the Hippocampus
Somogyi Péter
Medical Research Council Anatomical Neuropharmacology Unit, Dept. Pharmacology, University of Oxford

 The firing rates of neurons in the cerebral cortex vary between total silence and over 300 Hz. We have explored how distinct cell types change their firing rates in the cortex by recording and labelling single neurons in the hippocampus of freely moving and naturally sleeping rats. During spatial navigation, or the offline replay of spatial representations, pyramidal cell firing is rhythmic and phase-related to the local field potential in the theta, gamma and sharp wave related ripple(SWR)frequency ranges. The rhythmic firing of GABAergic interneurons in the hippocampus contributes to the synchronization of neuronal activity. Interneurons, innervating specific postsynaptic domains, selectively discharge at different rates, phase-locked to network oscillations in a cell type specific manner. All parts of pyramidal cells, except the axon initial segment, receive GABA from multiple interneuron types, each with distinct firing dynamics. Parvalbumin-expressing basket cells fire phase locked to field theta and gamma activity in both CA1 and CA3, and also strongly increase firing during SWRs in slow wave sleep, as do dendrite-innervating bistratified cells in CA1. Some other GABAergic cell types decrease their firing rate during sleep. The axon initial segment is exclusively innervated by axo-axonic cells, which preferentially fire after the peak of pyramidal layer theta when pyramidal cells are least active. The evolution of domain-specific GABAergic innervation was probably driven by the need of coordinating multiple glutamatergic inputs to pyramidal cells through temporally-distinct GABAergic interneurons, which independently change firing during different network states. I will demonstrate the key mechanism of coordination:a network state-dependent temporal redistribution of inhibition over distinct subcellular domains of pyramidal cells.